The present invention relates to a magnetic recording and reproducing apparatus having a function of detecting clogging of a magnetic head occurring when recording or reproducing video or audio signals on a magnetic recording tape through the magnetic head.
Clogging of a magnetic head is a phenomenon that dust or magnetic powder accumulates on the area contacting with a magnetic recording tape around a gap of the magnetic head. Clogging of magnetic head impedes normal contact of the magnetic head and the magnetic recording tape, or changes magnetic characteristics of the magnetic head. As a result, normal magnetic recording is disabled.
A technology of detection of clogging of magnetic head is disclosed, for example, in Japanese Laid-open Patent No. 59-104707 (laid open on Jun. 16, 1984). Herein, a reproducing magnetic head is disposed at a position on a rotary cylinder, different from that of a recording magnetic head, and clogging of the magnetic head in recording operation is detected by continuously monitoring the output of the reproducing magnetic head.
Including this example, in the method of detecting clogging of magnetic head, the amplitude value of reproduced signal at the time of deterioration of video recording quality and the envelope of reproduced signal are compared. In this method, when the envelope of reproduced signal is small, it is judged that recording abnormality due to clogging of magnetic head occurs, and a detection signal (alarm signal) is issued.
In this method, however, to detect clogging of magnetic head when recording, the magnetic head clogging detecting device is being operated continuously. It increases the power consumption of the magnetic recording and reproducing apparatus. In particular, in the case of a video tape recorder with a built-in camera which is often driven by a battery, this problem is troublesome. The increase in power consumption of the video tape recorder with a built-in camera has a substantial effect on the battery life.
A more specific example is given below.
Battery-driven portable video tape recorders with a built-in camera are widely used recently for broadcasting and professional use, in news gathering activities, and the like. In such applications, detection of clogging is necessary for recording securely. At the same time, in order to record for a longer time, it is also necessary to suppress the increase of power consumption due to detection of clogging.
Moreover, in the portable video tape recorder with a built-in camera, in order to reduce its size, the body of apparatus is required to be smaller. Downsizing of the body of apparatus is a troublesome condition for temperature rise due to power consumption in the electric circuit. Therefore, also for the purpose of reducing the size of the body of apparatus, it is demanded to suppress increase of power consumption due to detection of clogging.